RECHARGE OF THE MEMPHIS AQUIFER IN AN URBAN WATERSHED: IMPLICATIONS OF IMPERVIOUS SURFACES AND STREAM INCISION

The Memphis aquifer is the most important source for groundwater in western Tennessee; however, recharge processes to the aquifer are poorly understood. Previous studies have shown that in rural areas recharge to the aquifer occurs more efficiently in stream gullies with sand bottoms than in upland terraces. The same is expected in urban streams where the Memphis Sand is exposed in gullies and upland areas have substantial urban land use. Water balance research in Sandy Creek in Jackson, Tennessee, provides information regarding infiltration and potential recharge to the Memphis aquifer that may be typical of urban stream valleys where sandy Coastal Plain aquifers are exposed at the surface.

In the present study, hydrologic data have been collected from Sandy Creek since August 2017. The hydrologic analyses include soil and sediment grain-size; soil water measurement by soil moisture probes and neutron soil moisture meter; discharge estimates using stage-discharge relationships; and weather data from on-site and private weather stations. Preliminary data show that the upper reach of Sandy Creek is ephemeral with discharge present only during storm events. Stream flow rapidly dissipates following precipitation events due to infiltration into the stream beds. Soil moisture indicates a seasonal shift in water retained in the soil column with peak soil water storage during winter to early spring and steady drying through the fall. Monthly water balance estimates in the watershed indicate peak groundwater recharge during winter and early spring months with lesser contributions during the summer and fall. Most of the recharge is attributed to discharge losses in Sandy Creek and its tributaries, with little passing through the developed, silt-rich soils of the upland surfaces. However, approximately 45% of the length of Sandy Creek is in hydrologic contact with the Memphis Sand, which may decrease the potential for discharge loss to recharge. Recharge studies done on Sandy Creek and in rural areas in Western Tennessee show the importance of upland-stream discharge loss for recharge to the Memphis aquifer.